Dust gradually obscures the Sun during a blue-sky martian
sunset seen in a sequence of newly processed frames from
NASA's Mars Exploration Rover Opportunity.

"It's inspirational and beautiful, but there's good science
in there, too," said Dr. Jim Bell of Cornell University,
Ithaca, N.Y., lead scientist for the panoramic cameras on
Opportunity and its twin, Spirit.

The amount of dust indicated by Opportunity's observations of
the Sun is about twice as much as NASA's Mars Pathfinder
lander saw in 1997 from another site on Mars.

The sunset clip uses several of the more than 11,000 raw
images that have been received so far from the 18 cameras on
the two Mars Exploration Rovers and publicly posted at
http://marsrovers.jpl.nasa.gov. During a briefing today at
NASA's Jet Propulsion Laboratory, Pasadena, Calif., Bell
showed some pictures that combine information from multiple
raw frames.

A patch of ground about half the area of a coffee table,
imaged with the range of filters available on Opportunity's
panoramic camera, has soil particles with a wide assortment
of hues -- "more spectral color diversity than we've seen in
almost any other data set on Mars," Bell said.

Opportunity is partway through several days of detailed
observations and composition measurements at a portion of the
rock outcrop in the crater where it landed last month. It
used its rock abrasion tool this week for the first time,
exposing a fresh rock surface for examination. That surface
will be studied with its alpha particle X-ray spectrometer
for identifying chemical elements and with its Moessbauer
spectrometer for identifying iron-bearing minerals. With that
rock-grinding session, all the tools have now been used on
both rovers.

Dr. Ray Arvidson of Washington University, St. Louis, deputy
principal investigator for the rovers' science work,
predicted that in two weeks or so, Opportunity will finish
observations in its landing-site crater and be ready to move
out to the surrounding flatland. At about that same time,
Spirit may reach the rim of a larger crater nicknamed
"Bonneville" and send back pictures of what's inside. "We'll
both be at the rims of craters," he said of the two rovers'
science teams, "one thinking about going in and the other
thinking about going out onto the plain."

Not counting occasional backup moves, Spirit has driven 171
meters (561 feet) from its lander. It has about half that
distance still to go before reaching the crater rim. The
terrain ahead looks different than what's behind, however.
"It's rockier, but we're after rocks," Arvidson said.

Spirit can traverse the rockier type of ground in front of
it, said Spirit Mission Manager Jennifer Trosper of JPL. As it
approached the edge of a small depression in the ground
earlier this week, the rover identified the slope as a
potential hazard, and "did the right thing" by stopping and
seeking an alternate route, she said.

However, engineers are also planning to transmit new software
to both rovers in a few weeks to improve onboard navigation
capabilities. "We want to be more robust for the terrain
we're seeing," Trosper said. The software revisions will also
allow engineers to turn off a heater in Opportunity's arm,
which has been wasting some power by going on during cold
hours even when not needed.

As it heads toward "Bonneville" to look for older rocks from
beneath the region's current surface layer, Spirit is
stopping frequently to examine soil and rocks along the way.
Observations with its microscope at one wavy patch of
windblown soil allowed scientists to study how martian winds
affect the landscape. Coarser grains are concentrated on the
crests, with finer grains more dominant in the troughs, a
characteristic of "ripples" rather than of dunes, which are
shaped by stronger winds. "This gives us a better
understanding of the current erosion process due to winds on
Mars," said Shane Thompson, a science team collaborator from
Arizona State University, Tempe.

The rovers' main task is to explore their landing sites for
evidence in the rocks and soil about whether the sites' past
environments were ever watery and possibly suitable for
sustaining life.

JPL, a division of the California Institute of
Technology in Pasadena, manages the Mars Exploration
Rover project for NASA's Office of Space Science,
Washington, D.C. Images and additional information
about the project are available from JPL at
http://marsrovers.jpl.nasa.gov and from Cornell
University at http://athena.cornell.edu.